Naomi Feldman Learning and Overgeneralization Patterns in a Connectionist Model of the German Plural

The debate over the processing mechanism for inflectional morphology has focused largely on the German plural system because it seems to contain a minority default, a form that has low frequency but high productivity in diverse contexts. Child overgeneralization patterns, phonological similarity effects, restrictions on compounding, reaction times, and neural dissociations have all been used to argue that the German plural supports either the single-route model or the dual-route model of inflectional morphology. However, lack of modeling evidence limits the reliability with which researchers can attribute empirical patterns to either model. This thesis first examines whether a connectionist model can reproduce child acquisition and overgeneralization patterns. A three-layer perceptron is used to map singular forms to plural class, and the resulting learning and generalization patterns are compared with empirical data. Several similarities emerge, including early overgeneralization of the –e and –n plural classes, later overgeneralizations involving all plural classes, and poor learning and generalization of the umlaut plural class. The network also displays some key differences to child acquisition data, particularly lack of overgeneralizations on null plural target items. The next question involves the emergence of a default form in the network. This is examined by removing all familiar features from the input, yielding an input vector that contains only zeroes. Of ten trained networks tested with this vector, five produce an –n plural and two produce an –s plural, with one network activating both –n and –s and two networks producing no plural form at all. None of the other plural markers show signs of activation. Though the –n plural default is expected due to its high frequency in the training corpus, the –s plural cannot have emerged as a default form simply on the basis of frequency. These results suggest that the default-like characteristics of the German –s plural are compatible with the single-route model.